wireless mic forums

XD-V70L buzzing when video camera is using AC power supply
by lordloco on 2012-03-02 07:10:31.7350

Good afternoon all,

I have a bit of a tricky buzzing problem that I am experiencing when using the wireless plugged into a Canon LEGRIA HF200, but ONLY when the camera is using the AC power supply. I have a four of the XD-V70L systems and three of the Canons and this problem is happening accross them all so I know it is not an individual problem of either the Line 6 systems or the Canon video cameras.

Basically when I use the battery it is crystal clear, as soon as I plug the AC power supply into the camera a pulsing buzzing noise occursd

Has anyone had this problem and can help point me in the right direction to sort it out? I am stumped and my lack of knowledge means I dont know where to start to correct it. I do know that if I touch the AC power supply the buzzing becomes even worse (if that is any help?)

Many thanks in advance if anyone can help me at all!

Bradley

Re: XD-V70L buzzing when video camera is using AC power supply
by dboomer on 2012-03-02 09:57:43.9670

I could use a lot more detail please.

Is the camera wired to the V70 in any way? If so is it a true balanced connection? Is the buzzing in the audio line or mechanical?

Re: XD-V70L buzzing when video camera is using AC power supply
by RonMarton on 2012-03-02 17:59:32.8770

G'day Bradley...

As Don says, more detail would be helpful, but from what you've said, I'm guessing you're using the XD-V70 receivers for picking up audio without having to run cable all the way from the "action area" to the camera/s.

(Maybe something like "conference" work, with a few tripod-mounted cameras covering the "talking heads", their overlapping coverage allowing for tape or memory card changes ?)

From the effect of your hand on the power supply chassis, it seems to me that, when you mains-power the camera/s, both "un-balancing" and the dreaded "earth loop" are destroying the systems that prevent stray electro-magnetic fields from entering the mic inputs of the camera/s, resulting in the hum, buzz and "static" you've reported.

Here's the fix:

Balanced audio mic cables (three-pin XLF [female] to three-pin XLM [male] connectors) are the ONLY way to connect from the XLF (female) outputs on the V-70 receivers' back panels to the camera input/s. No guitar jacks, RCA's or other "domestic" leads, plugs and sockets.

If the cameras involved are "pro" or "semi-pro" models with XL mic inputs, this will be a breeze.

Many, however, only have a 3.5mm mini "headphone style" socket for connecting a "click-on" stereo electret microphone, and it's my guess that you're trying to adapt to something like this.

If so, the first thing would be to check if the manufacturer lists a 3.5mm mini jack to 2 x XL female (XLF) mic input "breakout" box as an accessory. Many do and if so, that's the best option.

If not, it gets a bit messy. You (or a technical buddy) will need to make adapters.

My preference would be for short "Y cords" that mimic such a break-out box, enabling you to decide whether a given mic is recorded onto track one (Left) or track two (Right). This can be really handy with different mics on different channels for later editing and mixing.

Chop off (gasp!) the RCA sockets, but mark the Left/Right colour code onto the individual wires before you do. Sometimes you can retain the coloured strain-reliefs and slide them higher up the cables as channel identifying boots ahead of the XLFs of your made-up adapter.

Solder the XLF's as follows: centre conductor of the "split" (formerly RCA) adapter cable to pin 2 of the XLF, shield (outer conductor) of the "split" (formerly RCA) adapter cable to pin 3 of the XLF.

Under NO circumstances allow anything to "short onto" or be connected to pin 1.

If the cameras only have MONO mini jack mic inputs, you'd only need to make single short adapter leads, each being "one half" of the above, without any need for colour coding. These would consist of mono 3.5mm plugs with their tips (centre conductors) connected to pin 2 of the XLFs and their shields (outer conductors) connected to pin 3 of the XLFs, ...with nothing connected or "shorting" to pin 1.

The fact that the cameras present a low-current couple of volts of electret-powering DC at their mic inputs is of very little consequence. It will be "shrugged off" by the XD-70 receivers.

It might also seem that not connecting to pin 1 implies lack of shielding, whereas the balanced mic cables are, in fact, shielded down their full length by virtue of their outer sheaths being connected to pin 1 at the receivers.

Re: XD-V70L buzzing when video camera is using AC power supply
by Sheriton on 2012-03-05 05:27:24.8640

On a slightly different tack, I recently tried to connect a normal wired dynamic mic to a Canon Legria camera. It worked fine when running on battery, but buzzed when plugged in to the mains. That rather scuppers the idea that it could be an earth loop. I didn't investigate further as running from battery was OK in that scenario but it does look like those particular cameras have issue with connecting microphones of any sort.

Re: XD-V70L buzzing when video camera is using AC power supply
by dboomer on 2012-03-05 07:51:04.0410

Sheriton ... thanks for the assist. I didn't have access to the camera to check it out.

Bradley... looks like this is a question for the camera's manufacturer.

Re: XD-V70L buzzing when video camera is using AC power supply
by RonMarton on 2012-03-05 07:51:48.8650

A much appreciated and well-made point, Sheriton...

But I'd like to take the liberty of qualifying it with an "Aah, ...not necessarily..."

Nonetheless, I guess I should have phrased the relevant bit in my third paragraph as "...possibly 'un-balancing' and/or the dreaded 'earth loop'..."

Two questions spring to my mind when you refer to your "normal wired dynamic mic":

Is the mic in question balanced XL male out? ...And...

If so, what is the wiring scheme of the XL female to mono 3.5mm plug adaptation you used for the Legria?

What I'm getting at is that we may now be talking about two different ways of obtaining this painful interference.

My suggestion for Bradley's problem is a scheme for ensuring the chassis earth of the XD-V receiver/s remains separate from that of the camera/s, the balanced signal pair being shielded as far as the adapter by pin 1 of receiver/s' XLM. That balanced pair is then unbalanced by camera via the short adapter, the camera using its chassis (and consequently the adapter's braided outer sheath) for signal "cold", one side of its DC supply and the all-important shielding.

It's a scheme I've successfully used many times for domestic gear in such "short run" situations, being a couple of metres of standard mic cable (handy to have, anyway...) with less than half a metre of adapter. It avoids the extra "bits of kit", weight and insertion loss of transformer-based adapters or the complexity of separately powered active converters.

With your wired mic, I'm wondering whether its adaptation to the 3.5mm mono plug may possibly have had the effect of unshielding it via the plug pack.

(I'm sure we all appreciate that it's these sorts of issues that have so many of us trying to find the extra cash for gear that actually has balanced XL inputs.)

Re: XD-V70L buzzing when video camera is using AC power supply
by Sheriton on 2012-03-07 05:17:28.3990

Continuing the slightly off topic discussion... The mic I refered to was wired directly to a 3.5mm jack - no adapters involved. Unbalanced cable (only a couple of meters long) wired signal to tip and shield to sleeve. ABout as simple as it gets.

(My "proper" cameras all have XLRs that just work, so it's always frustrating trying to use consumer kit that rarely works straight off.)

Re: XD-V70L buzzing when video camera is using AC power supply
by RonMarton on 2012-03-07 06:23:35.3880

Thanks for sticking with this, Sheriton...

...And heartfelt apologies if I created the impression that I had any doubts about your first (quite clearly correct) suspicion. I didn't. It was simply my clumsiness in trying to "get" as much info as possible.

Having passed this updated info around the "tech mob" here, considerable suspicion has now fallen on the "wall wart" plug-pack mains adapter supplied for the camera.

We reckon that, being a domestic "handycam" type of system, it's designed primarily for two main purposes "back at home":

Mains powered microphony would never have been part of the brief, so the cheap (probably un-regulated and un-filtered) plug-pack's propensity for cheerful radiation of spurious mains-derived RF "junk" via the "chassis earth" wasn't an issue.

If resources allow, here's an experiment with a view to finding a mains powering "cure"...

There are quite a few regulated (in some cases multi-voltage switchable) and cheap multi-adapter switched-mode plugpacks that have an "R.F. stopping lump" (choke and/or R/C filter) in the low-voltage output cable.

It would be worth trying (maybe a "borrowed"?) one, paying particular attention that it meets (or, preferably, exceeds) the current requirements of the camera and absolutely matches the voltage and polarity of the camera's D.C. input socket.

Should this effect a "cure", a few of these multi-purpose plug-packs would be a more practical and cheaper solution than lugging around something like gel-cell motorbike-style batteries in order to achieve the desired longer running times.

The information above may not be current, and you should direct questions to the current forum or review the manual.